For some other Toyotas with an engine immobilizer, it is possible for the dealer to reseed it without a recognized key (immobilizer system reset, and the dealer scantool can read the immobilizer data). However, for the Prius there is no reset available, nor can the data be read by the dealer's scantool. (This is at least for the 2001-2003 Prius, and the 2003 Sequoia, based on a Oct. 2003 TSB EL016-03.)DanMan32 said:About $200 purchased from your dealer (you might find one on EBay), plus programming your car to accept it, about another $50+
Now if you lost both keys, then the immoblizer supposedly needs to be replaced. Now you are talking $1000.
However I think I read a TSB where the immobilizer can be re-seeded by a dealer to accept new fobs without an existing one, though it depends on the dealer's willingness and knowlegability to do it.